The French Patent Nr 92 15473 discloses a data reading device in which inside of a reading head an expanded laser beam is used to read data stored on a magnetic tape. The magnetic tape supports a multiplicity of longitudinal tracks containing data. The expanded laser beam illuminates at least a part of the multiplicity of tracks simultaneously before being reflected and projected on a charge coupled device array (CCD). The CCD is divided in a number of cells each of which corresponds to a track read out with the expanded laser beam. For this reason a projection of the laser beam must be very precisely positioned on the CCD. It may happen that due to irregularities of the tracks on the magnetic tape, e.g. a transversal deviation the projection of the laser beam needs to be repositioned on the CCD. The disclosed device uses for this purpose a glass plate positioned between the magnetic tape and the CCD i.e. the laser beam crosses the glass plate before reaching the CCD. The glass plate may be moved in rotation around a rotation axis in such a way to reposition the projection of the reflected laser beam on the CCD. The glass plate is moved using an actuator which comprises an electromagnet and a permanent magnet. The electromagnet receives a tracking error signal from a servo loop which in a known manner determines errors in the positioning of the projection of the laser beam relative to the CCD. The movement and the position of the glass plate are solely controlled by the tracking error signal applied to the electromagnet. The lack of position information for the glass plate may be a drawback in some cases e.g. when a maximum and/or a minimum position of the glass plate and thus the activator need to be known. This is for example the case before a coarse positioning where the whole reading head (comprising a laser, optics to expand the beam, the glass plate, the CCD etc . . . ) is moved transversely to the tracks to read further tracks.